But appearing on Radio 5Live’s Pienaar’s Politics on Sunday, Mr Salmond said: “The phrase was not once in a lifetime, it was the opportunity of a lifetime, I said it on the Andrew Marr show, it’s just one of these collective myths that evolve.”

He later denied his denial, calling the story “bizarre”.

In a series of tweets, Mr Salmond said: “I wasn’t denying the once in a lifetime remark this morning, but rather pointing out that the interview in which it was actually made I described my view as ‘perhaps even once in a lifetime – OPPORTUNITY’.

“It was not some writ that a referendum is for life but an observation that perhaps an opportunity which might only occur once in a lifetime.”

On the radio this morning I was contrasting that remark from a television programme in 2014 with an election manifesto commitment from 2016…